The present invention relates to automobile wheel alignment systems. In particular, the invention relates to an angle sensor in an automobile wheel alignment system which uses a charge coupled device (CCD).
Proper alignment of wheels in an automotive vehicle is important for proper handling of the vehicle and proper tire wear. In addition, the proper alignment of the wheels will decrease fuel consumption as well as increase vehicle safety. The wheel alignment parameters which are measured and adjusted in order to achieve proper wheel alignment are camber, caster, steering axis inclination and toe.
The static toe angle of a wheel, at a specified wheel load or relative position of the wheel center with respect to a sprung mass, is the angle between a longitudinal axis and a line of intersection of wheel plane and road surface. The wheel is "toed-in" if the forward portion of the wheel is turned toward a central longitudinal axis of the vehicle, and "toed-out" if turned away. Accurate toe adjustment cannot be attained without properly calibrated measuring instruments.
Camber is defined as the angle which the wheel makes with respect to a vertical plane when looking at the wheel from either the front or the rear of the automobile. Any wheel of an automobile can have camber.
Caster is an angle which the steering axis of a steerable wheel (typically one of the front wheels) makes with respect to the vertical plane which is perpendicular to the longitudinal direction of the perpendicular to the longitudinal direction of the automobile.
Steering axis inclination (SAI) is the inclination of the steering axis with respect to a vertical plane which is parallel to the longitudinal direction of the automobile
Toe was originally defined as the difference of the distance between the front edges of two opposite wheels and the distance between the rear edges of the same two wheels. Toe can also be defined in terms of an angular relationship of the plane of a wheel (perpendicular to its turning axis) relative to a predetermined longitudinal vehicle axis. When the forwardmost portions of a pair of adjacent wheels are closer together than the rear portions of those wheels, they are commonly referred to as in a "toe-in" condition. When the rear portions of wheels are closer together than the front portions, the condition is commonly referred to as "toe-out."
Camber is a tire wearing angle and also affects handling of the automobile. Caster and SAI do not affect tire wear, but are important for directional control. Toe is a tire wearing angle and also affects the position of the steering wheel required in order to maintain the automobile along a straight line
Camber, caster and SAI are typically measured using one or more inclinometers which are attached to the wheel. With camber, the inclinometer measures the angle that the spindle makes with horizontal. With caster, the wheel is turned through an arc, and the difference in the camber readings is used to derive the caster value. SAI is measured in a manner similar to caster, except that the inclinometer used for the SAI reading is aligned at 90 degrees to the inclinometer used for reading camber and caster.
There is a continuing need for improved angle measurement systems which are easy to build and set up, and lower in cost.